Given the intense level of anti-Muggle prejudice in wizard supremacist movements (e.g. those of Voldemort and Grindelwald), it seems like there would be an equivalent slur to "Mudblood" to refer to Muggles. I can't recall if one is ever mentioned in either the books or the now prodigious additional material JK Rowling has been producing in interviews, Twitter, and Pottermore, and additional works like Beedle the Bard.
Is there a slur for Muggles in the Harry Potter universe?
There doesn’t seem to be any equivalent word to Mudblood for Muggles. The wizards we see who hate Muggles and use terms like Mudblood only ever call Muggles Muggles, not any other term. If there was a more derogatory term for Muggles, it seems likely at least one of them would use it. The Dark Lord himself, shortly after talking about Mudbloods, used the term Muggles for them.
“Silence,’ said Voldemort, with another twitch of Malfoy’s wand, and Charity fell silent as if gagged. ‘Not content with corrupting and polluting the minds of wizarding children, last week Professor Burbage wrote an impassioned defence of Mudbloods in the Daily Prophet. Wizards, she says, must accept these thieves of their knowledge and magic. The dwindling of the pure-bloods is, says Professor Burbage, a most desirable circumstance … she would have us all mate with Muggles … or, no doubt, werewolves …”
- Harry Potter and the Deathly Hallows, Chapter 1 (The Dark Lord Ascending)
No one else uses another term for Muggles, either. Presumably, this is because the word Muggle indicates something bad enough that there’s no need to invent a new word. To them, the word Muggles itself refers to something sufficiently and obviously bad, so it’s “automatically” an insult.
